Aileron control



Feb. l, 1944. E ZAP v AILERON coNTRoiI Filed July 7, 1941 /N VE N TOLEDWARD E ZAP @r #ARR/s, /r/Ec H, Foa-TIER d HARR/J E. F. ZAP

AILERON CONTROL Feb. 1, 1944.

Filed July '7, 1941 2 Sheets-Sheet 2 DEEE@ HARR/J, mec/7; F05 TER@ HRR/sPatented Feb. 1, 1944 UNITED sTATEs PATENT oEFlcE AILERON CONTROL EdwardF. Zap, Los Angeles, Calif.

Application July 7, 1941, Serial No. 401,319

3 Claims.

My invention relates to mechanical systems and mechanical arrangementsfor controlling ailerons or similar pairs of aerodynamic members thatare moved by a common means such as the usual control stick for oppositenight-control effects.

The present invention has the same purpose and the same general functionas the control arrangement set forth in my copending application SerialNo. 383,570, entitled Control system for airplanes, and will bedescribed as designed to control the same type of aileron.

At some stages in th operation of ailerons of the type hereincontemplated, it is required that one aileron be held immobile or lockedin some positive and automatic manner while the otherV aileron is in arange of effective positions. One

,object of my invention is to provide a control arrangement that willcause each aileron to function effectively when required and willlikewise provide a dwell to cause each aileron to be lockedautomatically against movement when required.

Other objects of my invention as set forth in my copending applicationinclude the following: to permit sensitivity of control immediatelyadjacent the neutral position of the control stick; to permit arelatively rapid increase in aileron angle as the control stickinitially departs from its neutral position; to permit the aerodynamicforces to be perceptible to the pilot through the control system; topermit balancing of oppOSite aerodynamic forces in the control systemthroughout a central range of control stick positions; to provide acontrol system that is not critical in adjustment; and to provide acontrol system in which looseness of operating connec tions does notresult in non-responsiveness 'of the.

control system.

The attainment of this group of objects under my concept involves whatmay be termed overlapping of the control 'zones of the control stick.Instead of having the neutral position of the control stick mark theprecise dividing line between two opposite control zones for operationof the two opposite ailerons, I arrange for the control zones to overlapso that movement of the control stick in a central range causes both thetwo ailerons to move simultaneously. One of the cbjects of the presentinvention is to provide means for permitting adjustment of the controlsystem with respect to the degree of such overlap.

Other objects and advantages of the invention will be apparent in mydetailed description to follow.

My control system includes a ilrst operating means rotatably responsiveto the control stick,

erating means on the one hand and each of the second and third operatingmeans on the other hand. Taking the rst operating means and the secondoperating means, by way o! example, the characteristic relationship maybe broadly described as involving the equivalent of a track means on oneof the two operating means that is engaged by the other operating means,the

track means having a portion concentric to the axis of rotation of thefirst loperating means to cause a dwell in the operation of the secondoperating means and having a second portion n onconcentric to said axiswhereby movement of the first operating means may be transmitted to thesecond operating means.

In the drawings: v

Fig. 1 is a diagrammatic view in perspective showing my inventionembodied in an aileron control system in an aircraft;

Fig. 2 is a rear elevation of the central group of operating members inthe system ;vv

Fig. 3 is a view partly in elevation and partly in section taken asindicated by the line H of F1g.2:

Fig. 4 is a section on an enlarged scale taken as indicated by the line4 4 of Fig. 2

Fig. 5 is a fragmentary view corresponding to a portion of Fig. 2showing an alternative ad- Y justment of the control system;'

Fig. 6 is a rear elevationsimilar to Fig. 2 showing the centraloperating members in a second form of the invention;

Fig. 'I is a view similar to Fig. '6 of a third form of the invention;and

Fig. 8 is a fragmentary cross section on an enlarged scale taken asindicated by the line 0-0 of Fig. 7.

The airplane shown in Fig. 1 has two wings I0 extending outwardly from afuselage Il and for rolling control is provided with a left ailerongenerally designated I2 and a right aileron generally designated I3. Forcontrol ofthe two ailerons a conventional control stick I5 may bemounted on a longitudinal torque tube I0, the torque tube beingrotatably supported by` suitable bearings such as the bearing I'I- shownin'Fig. 3.

Each of the ailerons I2 and I3 shown in Fig. 1v is,l by preference,constructed iis-@specifically de scribed in my previously mentionedcopending application. but it will be understood that the control systemis applicable to many other types of ailerons. For the purpose of thepresent disclosure, it is suiiicient to state that each ofthe aileronsI2 and I3 comprises a curved panel I8 with a plate 20 extending rearwardfrom its trailing edge. -At the ineilective position oi.' an aileron thepanel I8 is retracted into a slot (not shown) in the upper surface ofthe airplane wing, and the trailing plate 20 overlies the upper surfaceof the wing adjacent the slot. Any suitable means such as tracks orrollers (not shown) is provided to guide each of the panels .I8 throughvarious effective positions at which the panel extends to variousdegrees into the air stream. Extension of such an aileron into the airstream above a wins tends to lower the wing and thereby tends to rollthe aircraft on its longitudinal axis.

The aileron control system shown and 3 includes a ilrst operating meansin the form oi.' a rocker arm generally designated 2| that is adapted torotate about a longitudinal aids in response to lateral movement of thecontrol stick ill. In the depicted arrangement, the

rocker arm 2| is mounted on the torque tube I8 to rotate about the axisof the torque tube I8. Mechanically responsive to the first operatingmeans or rocker arm 2| is a second operating means generally designated22 for actuating the lett aileron i2, and likewise responsive is a thirdoperating means generally designated 23 for operating the right-handaileron |3. Each ci the second and third operating means 22 and 23 ismounted on the aircraft for a predetermined pattern oi movement, forexample, simple rotary movement or simple rectilinear movement. In thepresent and preferred arrangement, each of the operating means 22 and 23is mounted on a pivot bolt 25 for rotary movement and comprises a crankwith three arms, upper and lower arms 28 and 21 for transmittingmovement to the corresponding aileron, and an operating arm 30. Forconvenience, the second operating means .22 which actuates the leftaileron I2 will be referred to as the primary crank for the leftaileron, and the third operating means 23 vfor operating the rightaileron I3 will be referred to as the primary 'crank for the rightaileron.

To operate each of the ailerons I2 and I3 in response to movement of thecorresponding primary crank 22 or 23, I may employ a secondary three-armcrank 3| in each wing near the corresponding aileron. As indicated inFig. 1, each of the secondary cranks 3| has, a rearward arm 32operatively connected by a cable 33 to the upper arm 26 of thecorresponding primary crank 22 or 23, and has a forward arm 35 that isoperatively connected by a cable 36 to the lower arm 21 of thecorresponding rotary crank, the two cables being crossed and beingguided by suitable pulleys 31. A third arm 33 of each of the secondarycranks 3| is connected to the 'corresponding aileron by an operating rod40. It is apparent that clockwise rotation of the left primary crank 22,as viewed in the drawings, will cause corresponding counterclockwisemovement oi the secondary crank 3| in the left wing to cause the leftaileron I2 to be extended, 'and in similar manner counterclockwisemovement oi' the primary crank 23 for the right aileron will causeextension oi the right aileron I3.

Turning to Figs. 2 and 3 for more speciilc details oi' the construction,the drawings show that the rocker arm 2| on the torque tube I8 may be inthe form oi a casting providing a web or plate in Figs. l, 2,

portion 4I at its outer end. The casting has a cylindrical portion 42that embraces the torque tube I8 and is ilxedly attached thereto bydiametrically disposed bolts 43. Mounted on the rear face of the webportion 4| of the rocker arm 2l (the near face in Fig. 2) by suitablebolts 48 is e, track generally designated 43 for cooperation with theprimary crank 22 and mounted on the front face of the web by similarbolts is a second track generaly designated 41 for cooperation with theprimary crank 23. Each of the two tracks 48 and 41 forms a channelU-shaped in cross section into which extends a suitable complementaryconnecting means from the corresponding prlmary crank. In the particularconstruction shown in the drawings, the connecting means cooperatingwith the rear track 48 is a suitable roller 48 (Fig. 3) carried by theprimary crank 22, and the connecting means cooperating with the fronttrack 41 is a similar roller 58 carried by the primary crank 23. Asindicated in Fig. 3, each of the rollers 43 and 53 may be carried by asmall stub shaft 5I that is journaled in a suitable bearing. in theoperating arm 30 oi the corresponding primary crank.

The track 48 on the rear face of the rocker arm 2| has a left portion 53concentric to the axis of the torque tube I8 and a right portion |55that turns downward in a direction non-concentric to the axis of thetorque tube. When the control stick I5 is at its central position, thevarious parts being as indicated in Fig. 2, the roller 48 in the track46 is at or near the juncture oi the two portions 53 and 55 of thetrack. Substantial movement oi the control stick to the left resultingin equivalent leftward movement of the rocker arm 2| causes the roller48 to move downward along the non-concentric portion 55 of the track andthereby causes the primary crank 22 to rotate clockwise to extend theleft aileron I2. Contrary movement of the control stick from the neutralposition to swing the rocker arm 2| to the right causes relativemovement of the roller 48 along the concentric portion 53 of the track46- and thereby locks the primary crank 22 against rotation by virtue ofthe fact that any rotation would necessitate departure of the rollerfrom the line of curvature defined by the concentric portion of thetrack.

The forward track 41 on the rocker arm 2| cooperating with the secondroller 50 is similar to the rearward track but is oppositely disposed inthat the left portion 56 of the track is nonconcentric to the axis ofthe torque tube, and the right portion 51 is concentric to the torquetube axis. It is apparent that rightward movement of the control stickI5 to swing the rocker arm 2| clockwise causes the roller 50 to followthe non-concentric position of the track to rosition.

In the particular adjustment of the control mechanism illustrated byFig. 2, whenever the control stick is at its neutral position, the tworollers 48 and 50 are located approximately at the junctures of theconcentric and non-concen .tric portions of the corresponding tracks- 48and 41. If, as in some practices o! my invention, it

trol stick overlap for the purpose 'of achieving certain advantages, thecontrol system may be adjusted in the manner indicated by Fig. 5. InFig. 5, which represents the neutral position of the control stick I5,each of the rollers 48 and 56 is in the non-concentric portion of thecorresponding track at an appreciable distance from the juncture or thenon-concentric and concentricportions ofl the track. Such `an adjustmentof the control System results in each aileron being normally extended toan appreciable degree at the neutral position ofthe control stick,

.If the control stick is moved to the right, as viewed in Fig. 2, withthe control mechanism adjusted in the manner-shown in Fig. 5, the resultwill be vtwo distinct stages of aileron ope-, ation. In therst stageVoi? rightward movement from the neutral position of the control stick,the near'roller 46 carried by the leftcrank 22 initially moves up thenon-concentric portion 55 of required on the part of the pilot 'formanipuiation of the control stick-and gives the pilot a feel of hisship. Even a slight eeting predominance of force from one aileron overthe force from the opposite aileron is perceptible tothe pilot so longas the control stick is in the normal central portion of its range ofmovement. If'the two opposite forces from the ailerons are preciselybalanced with the control stick substantially at its neutral position,movement of the control stick in one direction by the pilot fox'- thepurpose of executing a maneuver results in upsetting the balance and thecontrol stick therefore resists -such movement. This resistance I givesthe pilot some indication of the relative magnitudes of the aileronforces and is conduthe track 46 to the juncture between thenonconcentric portion 55 and the concentric portion 53, this initialmovement of the roller 46 causing corresponding initial lowering of theleft aileron. In this first stage of leftward movement, simultaneouslythe far roller 50 controlling the right crank23 moves downthehun-concentric 'I portion 56 of, the track 41, thereby causingcorresponding upward movement of the right aileron. In this ilrst stageof rightward movement then, the two ailerons move oppositely. l' In thesecond stage, of rightward movement of the control stick from itsneutral position, the

`roller 46 controlling the left crank 22 moves into the concentricportion 53 of the track 46, thereby immobilizing the left aileron andmeanwhile the roller I) controlling the right crank 23 continues to movedown the non-concentric portion 56 oi.' the track 41, thereby continuingthe lifting of the right aileron. In this second stagef of rightwardmovement of the control stick, then,

v while the right aileron will be. immobilized, a second stage ofoperation in which the left aileron will continue to move downwardly andsimultaneously the right aileron will rise from its lowermost position,and a third stage in which the left aileron will be immobilized at itslowermost position while'the right aileron continues to rise to itsuppermost position.

The described mode of aileron operation has certain importantadvantages.

In the iirst place, when the pilot swings the control stick by asubstantial amount in either direction from neutral, thereby engenderingaerodynamic forces of relatively large magnitude,

one of the ailerons is mechanically locked to avoid transmitting thoseforces to-the control stick. In the second place, throughout a centralportion of the range of movement of the control stick. both aileronsfreely transmit forces to the control stick, the forces from the twoailerons being balanced against each other. This balancing of theopposed forces reduces the exertion cive to skillful flying. t

In the third place, in the central portion oi the control stick rang ofmovement, the airplane is 20 greatly responsive to the control stickbecause the two ailerons move simultaneously in oppo,

site directions in response to oscillation of the control stick. Achange in angle of the control stick qf one degree while the controlstick is in the central portion of its range of movement produces twicethe aileron eiect as a change of one degree in the position ofthecontrol stick while the control stick is outside of this centralprotion.

One of the features oi. the presentl invention is the conception of soconstructing the control system as to permit adjustment in the overlapof the control zones of the vcontrol stick. Any

means of 'adjustment may be provided that permits relative movement'ofthe two rollers 46 and 50vwith respect to the corresponding tracks 46and 41 independently oi' movements of the rockerV arm 2l. Thus thetracks 46 andV 41 may be adjustable on the rocker arm 2|, or the rollers4l and 56 may be adjustable relative to the primary cranks 22 and 23, orthe primary cranks may .be bodily movable for such adjustment. In mypreferred arrangement, I provide for -bodily movement of the two primarycranks 22 and 23.

As best shown in Fig. 4, each of the primary cranks 22 and 23 is mountedby a suitable bearing 56 on one of the previously mentioned pivot bolts25 and the pivot bolt in turn is carried by a bracket 60. A base 6I ofthe bracket 60 lies` against a complementary support member 62 that isunitary with the aircraft structure, the baseof the bracket beingsecured to .the support member by suitable means such as bolts 63.Rivets may be substituted for the bolts if desired. To receive the bolts63, the base 6I of the bracket.

is provided .with a series of holes 65 of given spacing, and the supportmember 62 isprovided with a complementary series of holes 66 of dif--ferent spacing, the arrangement being such that various holes of oneseries register withy various holes of the other series at differentpositions of adjustment of the bracket 60 relative to the supportmem-ber 62. For example, the holes 65 in the base member may beone-fourth of an inch in diameter and spaced at one-half inch center tocenter, while the holes 66 in the support member maybe one-fourth of aninch in diameter and spaced at iive-eighths of Van inch center tocenter. In such an arrangement the bracket 6I may be moved through anumber of successive positions by shifts-of one-,eighth inch and at eachposition pairs of holes at two inch spacing will register to receivethe4 bolts 63.` Whenever a change is desired in the overlapping relationof the control zones of the control stick, it is necessary merely toremove the bolts 88 anchoring the two brackets and then to replace thebolts at new positions in the two brackets.

In the second form of my invention shown in Fig. 6, a rocker arm 18 onthe torque tube i8 corresponding to the previously described rocker arm2| carries on its rear face a track generally designated 'II comprisingtwo sections in end to end abutment, the two sections being separatelyattached to the rocker arm by suitable vbolts 18. The track 1| has acentral portion 13 cencentric to the axis of the torque tube and has twoend portions and 'I6 that turn downward in directions non-concentric tothe torque tube axis. In this second form of the invention, a primarycrank 11 for actuating the left arm is placed on the right side of therocker shaft instead of the left and a similar yprimary crank 18 for theright aileron is located to the left of the rocker arm. Each of thesetwo primary cranks 11 and 18 has upper and lower arms 88 and 8|respectively for connection by suitable cables 82 and 88 to thepreviously described secondary cranks 8| in the airplane wings. Each ofthe upper arms 881 is connected to the forward arm 880i thecorrespending' secondary crank 8|, and each of the lower arms 8| of' theprimary crank is likewise connected to the rearward arm 82 of thesecondary crank. Counterclockwise rotation of the primary crank 11causes similar clockwise rotation of the corresponding secondary crank8| in the left wing, and clockwise rotation of the pri mary crank 18causes corresponding clockwise rotation of the'corresponding crank 3| inthe right wing. Each of the primary cranks 11 and 18 may be mounted inthe manner previously described on a pivot bolt 85 carried by anadjustable bracket 88.

In Fig. 6, representing the normal neutral position of the control stickI5, a roller 81 on an operating arm 88 of the primary crank 11 engagesthe track 1| at the entrance to the end portion 15 of the track, and aroller 88 on an operating arm 98 of the primary crank 18 is likewise inengagement with the track at the entrance to the end portion 18 of thetrack. Substantial movement of the rocker arm 18 to the left, as viewedin Fig. 6, causes the roller 81| to follow the end portion 15 of thetrack, thereby causing the primary crank 11 to rotate counterclockwiseto extend the left aileron I2, and meanwhile the roller 88 of theprimary crank 18 moves into the central concentric portion 13 of thetrack to lock the right aileron in retracted disposition. Conversely,substantiai movement o! the rocker arm to the 'right causes clockwiserotation of the primary crank 18 to extend the right aileron I3 andcauses the left aileron to be locked in retracted position. It isapparent that the two brackets 88 may be adjusted in the mannerheretofore described to cause' the two operating zones of the controlstick to overlap to various degrees.

In the third form of the invention shown in rear view in Fig. 7 and insection in Fig. 8, a rocker arm 8| corresponding to the previouslymentioned rocker arm 18 is mounted on the torque tube |8 for rotationabout the torque tube axis. To the right of the rocker arm 8| a primarycrank 82 corresponding to the primary crank 11 of Fig. 6 is mounted by apivot bolt 83 on an adjustable bracket 85, and toV the'left of therocker arm a primary crank 98 corresponding to the previously mentionedprimary crank 18 is mounted by a pivot bolt 83 on a second adjustablebracket 88. The primary crank 82 that 75 operates the left aileron andthe primary crank 88 that operates the right aileron are operativelyconnected to corresponding secondary cranks in the lairplane wings aspreviously described with reference to Fig. 6, an upper arm 81 of eachprimary crank being connected by a cable 88 to the forward arm 85 of thesecondary crank and a lower arm |88 oi each primary crank being con--nected by a cable |8| tothe rearward arm 82 of the correspondingsecondary crank.

The rocker arm 8| carries a rearward roller |82 for controlling anoperating arm |88 of the primary crank 82 and a forward roller |88coaxial with the rearward roller for controlling an operating arm |88 ofthe primary crank 88. The rearward roller |82 is in engagement with atrack |81 that is mounted on the operating arm |88 by suitable bolts,and in similar manner the forward roller |88 engages a track I I8 on theoperating arm |88. each of the tracks |81 and II8 has a portion IIIconcentric to the axis of the torque tube I8 and an end portion ||2 thatis non-concentric to the torque tube axis. Movement of the rocker arm 8|to the left, as viewed in Fig. 7, causes 'the pri-- mary crank 82 torotate counterclockwise for extension of the left aileron and movementof the rocker arm 8| to the right from neutral position causestheprimary crank 88 to rotate clockwise to extend the right aileron I3.It is apparent that this third arrangement will operate the two aileronsin the same manner as the second arrangement depicted in Fig. 6 and maybe adjusted in the same manner.

f posed on the aircraft for opposite control effects;

a manual control member movable from a neutral position in one directionthrough a iirst control zone and in the opposite direction through asecond control zone for opposite Hight-control eiects; a first meanspivotally movable about an axis in response to movement of said controlmember; a second means operatively connected to one of said aerodynamicmembers; a track means on one of said first and second means; a

. connecting means on the other of said iirst and second means inengagement with said track means for relative movement along the trackmeans, a portion of said track means/being nonconcentric to said axis tocooperate with said connecting means to actuate said second means over aportion of the range of movement of said first means, another portion ofsaid track means being concentric to said axis to cooperate with saidconnecting means to lock said second means against movement over asecond portion of the range of movement of said first means; a thirdmeans operatively connected to the other oi said aerodynamic members; asecond track means on one of said ilrst and third means; and a second'connecting means on the other of said iirst and third means inengagement with said second track means for relative movement along saidsecond track means, a portion of said second track means beingnon-concentric to said axistocooperate with said second connecting meansto actuate As clearly indicated in Fig. 1,

said third means over a portion of the range of movement oi' said ilrstmeans, another portion of said second track means being concentric tosaid axis to cooperate with said second connecting means to lock saidthird means against movement over a second portion of the range ofmovement of said rst means, said two track means being oppositelydisposed, said two connecting means having normal positions in thenon-concentric portions oi the corresponding track means spaced from theconcentric portions thereof when said manual control member is in saidneutral position whereby both said second and third operating means areresponsive in opposite operative directions to initial movement of saidmanual control member in either direction from said neutral position o1'the manual control member, and whereby continuation of such movementresults in subsequent immobilization of one of said second and third,operating means and continued movement of the other.

2. A control system for an aircraft comprising in combination: twoaerodynamic members disposed on the aircraft for opposite controleffects; a manual control member movable from a neutral position in onedirection through a first control zone and in the opposite directionthrough a second control zone for opposite flight-control effects; a rstmeans pivotally movable about an axis in response to movement of saidcontrol member; a second means operatively connected to one of saidaerodynamic members; a track means on one of saidilrst and second means;a connecting means on the other of said first and second means inengagement with said track means for relative movement along the trackmeans, a portion of said track means being nonconcentric to said axis tocooperate with said connecting means to actuate said second means over aportion of the range of movement oi said iirst means, another portion ofsaid track means being concentric to said axis to cooperate with saidconnecting means to lock said second means against movement over asecond portion of the range of movement of said llrst means; a thirdmeans operatively connected to the other of said aerodynamic mem-bers; asecond track means on one of said nrst and third means; a secondconnecting means on the other of said rst and third means in engagementwith said second track means for relative movement along said secondtrack means, a portion of said second track means being non-concentricto said axis to cooperate with said second connecting means to actuat'esaid third means over a portion of the range of movement of said firstmeans, another portion oi.' said second track means being concentric tosaid axis to cooperate with said second connecting means to lock saidthird means against movement over a second portion of the range ofmovement of said iirst means, said two track means being oppositelydisposed, said two connecting means having normal positions in thenon-concentric portions of the corresponding track means spaced from theconcentric portions thereof when said manual control member is in saidneutral position whereby both said second and third operating means areresponsive in o pposite operative directions throughout a centralportion of the range oi movement of said manual control member, andvwhereby movement of said manual control member out of said centralportion oi' its range results in immobilization of one of said second.and-third operating means and continued movement of the other; andmeans to vary the extent of said central portion oi the range ofmovement of said control member, said varying means comprising'means tocause said normal positions of said connecting means to shift along saidnon-concentric portions oi the corresponding track means.

3. A control system for an aircraft comprising in combination: twoaerodynamic members disposed on the aircraft for opposite controleilects;

a manual control member movable from a neutral position in one directionthrough a first control zone and in the opposite direction through asecond control zone for opposite night-control effects; a iirst meanspivotally movable about an axis in response to movement of said controlmember; a second means operatively connected to one of said aerodynamicmembers; a track means on one of said ilrst and second means; aconnecting means on the other of said first and second means inengagement with said track means for relative movement along the trackmeans, a portion of said track means being nonconcentric to said axis tocooperate with said connecting means to actuate said second means over aportion of the range of movement of said first means, another portion ofsaid track means being concentric to said axis to cooperate with saidconnecting means to lock said second means against movement over asecond portion of the range of movement of said iirst means; a thirdmeans operatively connected tothe other of said aerodynamic members; asecond track means on one of said first and third means; a secondconnecting means on the other of said irst and third means in engagementwith said second track means for relative movement along said secondtrack means,a portion of said second track means being non-concentric tosaid axis to cooperate with said second connecting means to actuate saidthird means over a portion of the range of movement of said first means,another portion oi' said second track means being concentric to saidaxis to cooperate with said second connect-- ing means to lock saidthird means against movement over a second portion of the range o1'movement of said rst means, said two track means being oppositelydisposed, said two connecting means having normal positions in thenon-concentric portions of the corresponding track means spaced from theconcentric portions thereof when said manual control member is in saidneutral 53 position whereby both said second and third operating meansare responsive in opposite operative directions throughout a centralportion of the range of movement of said manual control member, andwhereby movement of said manual control member out of said centralportion of its range vresults in immobilization of one oi' said secondand third operating means and continued movement oi the other; andstationary means pivotally supporting said second and third operatingmeans respectively, said stationary means being adjustably movable tovary saidnormal positions of the connecting means along saidnonconcentric portions of the corresponding track means, therebyto varythe extent of said central portion of the range of movement of saidmanual control member.

EDWARD F. ZAP.

